The present invention relates generally to electronic components such as connectors, switches and sensors for conducting electrical current. The present invention also relates generally to devices for neutralizing or eliminating static electrical charge buildup from a surface.
In particular, the present invention relates to such electronic components and static eliminator devices which are useful in various types of machines and other applications which require such components and devices for their proper operation. More specifically, the electronic components and static eliminator devices of the present invention each generally comprise a pultruded composite member having a plurality of small generally circular cross section conductive fibers in a polymer matrix where the fibers are oriented in a direction parallel to the axial direction of the member and are continuous from one end of the member to the other, with one end of the member having a fibrillated brush-like structure. The electronic components described herein are particularly well suited for low energy electronic/micro electronic signal level circuitry typified by contemporary digital and analog signal processing practices, while the static eliminator devices discussed below are ideally designed for removing or neutralizing static electrical charge buildup from dielectric substrates, such as copy paper. Typical of the type of machines which may use such electronic components and devices are electrostatographic printing machines.
In electrostatographic printing apparatus commonly used today a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface, such as copy paper, which is transported through the electrostatographic printing apparatus. The toner image may be permanently affixed to the copy paper by heating or by the application of pressure.
In commercial applications of such electrostatographic printing apparatus, the photoconductive member has typically been configured in the form of a belt or drum moving at high speed in order to permit high speed multiple copying from an original document. Under these circumstances, the moving photoconductive member must be electrically grounded to provide a path to ground for all the spurious currents generated in the xerographic process. This has typically taken the form of a ground strip on one side of the photoconductive belt or drum which is in contact with a grounding brush made of conductive fibers. Some brushes suffer from a deficiency in that the fibers are thin in diameter and brittle and therefore the brushes tend to shed which can cause a problem in particular with regard to high voltage charging devices in automatic reproducing machines in that if a shed conductive fiber comes in contact with the charging wire it has a tendency to arc causing a hot spot on the wire resulting in melting of the wire and breaking of the corotron. This is destructive irreversible damage requiring unscheduled service on the machine by a trained operator. Also, the fiber can contaminate the device and disrupt uniformity of the corona charging.
Furthermore, in commercial applications of such electrostatographic printing apparatus it is necessary to distribute power and/or logic signals to various sites within the machine. Traditionally, this has taken the form of utilizing conventional wires and wiring harnesses in each machine to distribute power and logic signals to the various functional elements in an automated machine. In such distribution systems, it is necessary to provide electrical connectors between the wires and components. In addition, it is necessary to provide sensors and switches, for example, to sense the location of copy sheets, documents, etc. Similarly, other electrical devices such as interlocks, etc. are provided to enable or disable a function.
The most common devices performing these functions have traditionally relied on metal-to-metal contacts to complete the associated electronic circuit. While this long time conventional approach has been very effective in many applications, it nevertheless suffers from several difficulties. For example, one or both of the metal contacts may be degraded over time by the formation of an insulating film due to oxidation of the metal. This film may not be capable of being pierced by the mechanical contact forces or by the low energy (5 volts and 10 milliamps) power present in the circuit. This is complicated by the fact that according to Holm, Electric Contacts, page 1, 4th Edition, 1967, published by Springer-Verlag, no amount of force if the contacts are infinitely hard can force contact to occur in more than a few localized spots. Further, corroded contacts can be the cause of radio frequency interference (noise) which may disturb sensitive circuitry. In addition, the conventional metal to metal contacts are susceptible to contamination by dust and other debris in the machine environment. In an electrostatographic printing machine, for example, toner particles are generally airborne within the machine and may collect and deposit on one or more such contacts. Another common contaminant in a printing machine is a silicone oil which is commonly used as a fuser release agent. This contamination may also be sufficient to inhibit the necessary metal-to-metal contact. Accordingly, the direct metal-to-metal contact suffers from low reliability particularly in low energy circuits. To improve the reliability of such contacts, particularly for low energy applications, contacts have been previously made from such noble metals as gold, palladium, silver and rhodium or specially developed alloys such a palladium nickel while for some applications contacts have been placed in a vacuum or hermetically sealed. In addition, metal contacts can be self-destructive and will burn out since most metals have a positive coefficient of thermal conductivity and as the contact spot gets hot due to increasing current densities it becomes more resistive thereby becoming hotter with the passage of additional current and may eventually burn or weld. Final failure may follow when the phenomena of current crowding predominates the conduction of current. In addition to being unreliable as a result of susceptibility to contamination, traditional metal contacts and particularly sliding contacts owing to high normal forces are also susceptible to wear over long periods of time.
As previously mentioned, the copy paper or similar support surface must be transported to an appropriate location within the electrostatographic printing apparatus prior to transferring the toner image from the photoconductive insulating member. After the toner image is transferred, the copy paper is then transported through the electrostatographic printing apparatus for subsequent electrostatographic operations or discharge of the copy paper. The guide members and transport mechanisms utilized for the copy paper transporting process produce frictional contact across the copy paper, which typically results in the generation of triboelectric charges. Additionally, electrical charges intentionally produced by the electrostatographic printing apparatus are also induced upon the copy paper. These electrical charges may be either positive or negative in polarity. Due to its dielectric characteristics, the copy paper or similar support surface typically will accept and hold these charges.
The buildup of these electrical charges greatly hinders handling and transportation of the copy paper. Since copy paper is thin and flexible, the static electric charge will cause the copy paper to be repelled from some areas or components of the electrostatographic printing apparatus and attracted to others. Further, the static electric charge will likely cause multiple sheets of copy paper to stick together, and potentially jam the electrostatographic printing apparatus during operation. An additional nuisance of static electric charge buildup on multiple sheets of copy paper is the resultant electric shock which may be discharged to an operator of the electrostatographic printing apparatus. Finally, static electric charge buildup on the copy paper is known to be detrimental to image quality. That is, toner particles and other contaminants which are present in the electrostatographic printing apparatus will adhere to the charged copy paper, thus dulling and degrading background quality.
Several methods and devices have been proposed for the elimination or neutralization of static electrical charge buildup on copy paper. An earlier concept was an independently powered device which ionized the air surrounding the copy paper, thus providing a grounding path. However, this device was expensive to manufacture and operate, and was a producer of ozone. A later concept utilized grounded metallic tinsel positioned to drag across the surface of the copy paper as the copy paper was discharged from the copier apparatus. This "tinsel" device was not totally effective in discharging the sheet, and therefore, did not assist in fully reducing the difficulty in handling the electrically charged copy paper within the electrostatographic printing apparatus. Further, the tinsel would tend to scratch the newly-formed image on the copy paper surface.
Recently, various embodiments of brushes have been developed for use within electrostatographic printing apparatus to assist in eliminating static electrical charge buildup on copy paper. Generally, these static eliminator brushes are strategically positioned within the electrostatographic printing apparatus, such that the copy paper passes in contact with grounded fibers of the static eliminator brush prior to being handled by a transporting mechanism. While brush-type static eliminators have proven to be effective in eliminating electrical charge, several disadvantages have been identified due to the materials and construction used.
For example, static eliminator devices using metallic brush fibers are known to have a limited effective life after continued operation. Alternatively, static eliminator brushes have been developed with conductive carbon fibers of relatively long length, i.e., 15-25 mm, to ensure flexibility of the brush fibers. However, these relatively long conductive carbon fibers tend to shed from the brush due to the inherent brittleness of the thin carbon fibers. As with the photoconductive member grounding brushes discussed above, when these relatively long conductive carbon fibers contact and bridge the charging wire of one of the several high voltage charging devices common to electrostatographic printing apparatus, there is a tendency to arc and damage the charging wire. This damage to the wire is destructive and irreversible, thus disrupting the uniformity of the charging device and requiring unscheduled service to the apparatus. Carbon fibers of higher electrical resistivity have been developed and utilized to minimize arcing within the electrostatographic printing apparatus; however, for a variety of reasons, static eliminator brushes of higher resistivity and lower conductivity are not always desirable.